Tires are sometimes prepared with treads of rubber compositions comprised of diene-based elastomers which contain reinforcement as carbon black or as silica in combination with a coupling agent to aid in coupling the silica to diene-based elastomers.
A coupling agent for such purpose usually has a moiety which is reactive with hydroxyl groups on the silica (e.g.: silanol groups) and another moiety which is interactive with diene-based elastomers. Such philosophy is well known to those having skill in such art.
Representative of such coupling agents are, for example, bis-(3-alkoxysilanealkyl) polysulfides which contain from two to eight sulfur atoms in their polysulfide bridges, with an average of from 3.5 to 4.5 for a tetrasulfide material and an average of about 2 to about 2.6 for a disulfide material. For such coupling agent, the alkoxysilane is available to react with the silanol groups on the silica.
In the description of this invention, the term "phr" as used herein, and according to conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber elastomer". In the description of this invention, the terms "rubber" and "elastomer" can be used interchangeably, unless otherwise distinguished. The terms "rubber composition", "compounded rubber" and "rubber compound" can be used interchangeably to refer to "rubber which has been blended or mixed with various ingredients and materials" and the terms "cure" and "vulcanize" may also be used interchangeably herein, unless otherwise noted and such terms are well known to those having skill in the rubber mixing or rubber compounding art.